Acnida cannabina var. prostrata (Uline & W.L. Bray) Fernald
Acnida cannabina var. subnuda (S. Watson) Fernald
Acnida concatenata (Moq.) Small
Acnida subnuda (S.Watson) Standl.
Acnida tamariscina var. concatenata (Moq.) Uline & W.L.Bray
Acnida tamariscina var. prostrata Uline & W.L.Bray
Acnida tamariscina var. subnuda (S.Watson) J.M.Coult.
Acnida tamariscina var. tuberculata (Moq.) Uline & W.L.Bray
Acnida tuberculata Moq.
Amaranthus altissimus Riddell nom. inval.
Amaranthus ambigens Standl.
Amaranthus cannabinus var. concatenatus Moq.
Amaranthus rudis J.D.Sauer
Montelia tamariscina (Nutt.) A. Gray
Amaranthus tuberculatus, commonly known as roughfruit amaranth,[4]rough-fruited water-hemp,[5]tall waterhemp, or common waterhemp,[6][7] is a species of flowering plant. It is a summer annual broadleaf with a germination period that lasts several months.[8]
Tall waterhemp has been reported as a weed in 40 of 50 U.S. states.[9]
A distinguishing characteristic of tall waterhemp that sets it apart from similar members of the genus Amaranthus is the lack of hair on its stems and leaves. This characteristic gives the plant a bright, glossy appearance.
The leaves of tall waterhemp tend to be long and narrow.
The stem is typically erect and slender and can be up to three feet long. The color of the stem is green or red.[8]
Tall waterhemp is a dioecious plant. The seedhead branches in the female are numerous, short, and smooth. The male seedhead branches are fewer, longer, and more slender than those of the female.
The species has terminal spike inflorescences and very short bracts with simple to highly branched flowers. Seed produced is reddish to black and less than 1/32 inch in diameter.[10]
Tall waterhemp predominantly grows in wet habitats, such as ponds, marshes, lakes, creeks, and other riparian zones. It also thrives along roadways and railroads as well as agricultural fields.[11] It can grow in a variety of climates, as evidenced by its widespread range.
Tall waterhemp is a summer annual that produces a large number[quantify] of very small[quantify] seeds. It is considered an r-strategist. Emergence can span several months and often occurs later in the season than other annual weeds, allowing the weed to evade typical weed control strategies such as herbicide application and tillage.[8] One study observed 80% emergence not occurring until ten weeks after the initial emergence.[13] Extreme temperatures have little effect on seed viability. Germination occurs typically after soil temperature alternation, as this is required to break seed dormancy.[14] Waterhemp has been found to germinate in a wide range of soil and temperature conditions.[15] It has been found to germinate 17 years after seed set.[16]
While tall waterhemp cannot self-pollinate, due to having separate male and female plants, it does not require any vectors for pollination.[15] This allows for wind pollination over large distances, generating a large amount of genetic diversity. Another factor contributing to genetic diversity is the large amount of seed produced. Tall waterhemp in competition with soybean has been reported to produce from between 300,000 and 5,000,000 seeds per plant.[17] Tall waterhemp also has a rapid growth rate, 50–70% greater than other annual weeds.[18]
Interspecific hybrids of tall waterhemp and Amaranthus hybridus have been observed in experimental fields[19] but have not been observed in agronomic fields.[20]
InNorth America, tall waterhemp is considered a major weed of agricultural fields and other disturbed habitats.[11] The Southern Weed Science Society includes tall waterhemp on their list of weed species.[21] However, it is not listed on the federal noxious weed list or any state lists in the United States.[22]InEurope and other continents where the species has been introduced, naturalization is an infrequent occurrence.[11]
Because of the long germination window for tall waterhemp, a single herbicide application is unlikely to be an effective control strategy.[23]Michigan State University Extension recommends a preemergence application followed by one or more postemergence applications.[8][23] Some populations of tall waterhemp have been reported resistant to acetolactate synthase inhibiting (ALS) herbicides[23] and the triazines,[23] with some individual weeds being resistant to both herbicide groups.[23] Resistance to acifluorfen and other diphenyl ether herbicides has been reported.[8][15] Even more alarming is the emergence of waterhemp resistant to the latest generation of herbicides, HPPD inhibitors.[24][23] Furthermore, waterhemp at a site in Nebraska was found to be resistant to 2,4-D, a phenoxy herbicide.[25][23]
According to Bob HartzlerofIowa State University, the most effective control of tall waterhemp is achieved by cultural practices that promote growth of the desired vegetation.[15]
^USDA, NRCS (n.d.). "Amaranthus tuberculatus". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 7 January 2016.
^Weekly emergence of waterhemp and giant ragweed in Ames, IA. 2000. Sandell, Buhler and Hartzler, Iowa State University
^Leon RG, Knapp AD, Owen MDK (2004) Effect of temperature on the germination of common waterhemp (Amaranthus tuberculatus), giant foxtail (Setaria faberi), and velvetleaf (Abutilon theophrasti). Weed Science: Vol. 52, No. 1 pp. 67–73
^Burnside, O.C., R.G. Wilson, S.Weisberg and K.G. Hubbard. Seed longevity of 41 weed species buried 17 years in eastern and western Nebraska. Weed Sci. 44:74-86.
^Hartzler, R.G., B.A. Battles and D. Refsell. 2004. Effect of common waterhemp emergence date on growth and fecundity in Glycine max. Weed Sci. 52.
^Horak, M.J. and T.M. Loughin. 2000. Growth analysis of four Amaranthus species. Weed Sci. 48:347-355.
^Trucco, F., M.R. Jeschke, A.L. Rayburn, and P.J. Tranel. 2005. Amaranthus hybrids can be pollinated frequently by A. tuberculatus under field conditions. Heredity 94:64–70.
^Rayburn, A. Lane, McCloskey, R., Tatum, Tatiana C., Bollero, German A., Jeschke, Mark R., Tranel, Patrick J. Genome Size Analysis of Weedy Amaranthus Species. Crop Sci 2005 45: 2557-2562
^Southern Weed Science Society. 1998. Weeds of the United States and Canada. CD-ROM. Southern Weed Science Society. Champaign, Illinois
^Bernards, Mark L.; Crespo, Roberto J.; Kruger, Greg R.; Gaussoin, Roch; Tranel, Patrick J. (2012). "A Waterhemp (Amaranthus tuberculatus) Population Resistant to 2,4-D". Weed Science. 60 (3): 379–384. doi:10.1614/WS-D-11-00170.1. S2CID86730513.
